Simplified a bit further (in order to bring it to lifesaving service as early as possible), the first generation of “ambulance mule” might just be a covered pod with legs, leaving what might be very complicated stretcher-loading work to other humans on-site. A mechanized infantry unit could have a couple of these folded up in the bay of every personnel carrier, ready to run “home” at a moment’s notice. For squads operating away from vehicles, a larger “cargo mule” bot could carry one or more ambulance mules along with other provisions. [*]

I suppose one endpoint is for every soldier to wear some kind of exoskeleton or frame pack that can, if needed, sprout legs and drag its owner/passenger to safety, while administering basic first aid (on its own or via telepresent medics) and providing some degree of protection from the environment.

I expect that we will see a very wide variety in the types of quadrupedal robots in military service over the next couple of decades, with tradeoffs on factors like speed vs. payload capacity vs. on-board decisionmaking ability vs. armament vs. power efficiency vs. reconnaissance capabilities vs. size vs. stealthiness. It will be interesting to see how the various service branches adapt to manage that diverse robot ecosystem and operate effectively within / alongside it.

[* - If an ambulance mule carries its own payload of surgical robots, and if a larger cargo mule that carries ambulance mules also rides into a theater of operations on a robotic helicopter or a robotic ship, then is there even a name for that??]

http://en.wikipedia.org/wiki/General_Atomics_MQ-9_Reaper

http://www.youtube.com/watch?v=COL0xpZw6Sc&feature=player_embedded